The present invention relates to a liquid crystal display device, and in particular, to a drive system and a drive circuit for a liquid crystal display in accordance with a time division system in which a source signal generating circuit is mounted.
The mobility of poly-Si (polysilicon) under electrical field effects is greater than the mobility of amorphous Si under electrical field effects, which is approximately 0.5 to 1 cm2/Vs, by approximately several tens to 200 cm2/Vs. Therefore, peripheral circuits, such as signal circuits and scanning circuits, can be formed on the same substrate as the liquid crystal display portion using poly-Si TFT's. In addition, periphery circuits and a liquid crystal display portion can be formed on the same substrate using poly-Si TFT's, and thus, connection with external peripheral circuits, such as source signal generating circuits, becomes unnecessary, and it becomes possible to implement a liquid crystal display device with high resolution. In the case where a liquid crystal display device with high precision and high resolution is implemented, however, the clock frequency in periphery circuits, particularly signal circuits, increases to several tens of MHz. However, the operation frequency in peripheral circuits using poly-Si TFT's is as low as approximately several MHz to approximately 10 MHz, and thus, it is difficult to implement liquid crystal display devices with high resolution where peripheral circuits are formed around the liquid crystal display portion.
Therefore, an RGB time division driving system where time division switches provided on the same substrate as the liquid crystal display portion and a driver IC are used, for example, has been proposed as a means for implementing a liquid crystal display device with high precision and high resolution using poly-Si TFT's. As described in Japanese Unexamined Patent Publication 2000-275611 (Patent Document 1), this system uses a source signal generating circuit as a signal circuit which requires high-speed operation. The source signal generating circuit is operable with a high frequency of several tens of MHz, and a number of display signals can be outputted collectively. In liquid crystal display devices using an RGB time division driving system, one output terminal for the source signal generating signal and three drain lines (drain lines corresponding to each pixel: R, G and B) included in the liquid crystal display portion are connected via time division switches provided on the same substrate as the liquid crystal display portion. In the RGB time division driving system, one horizontal period is time divided into three periods, and one drain line is selected from among three drain lines corresponding to R, G and B during each period in sequence. The source signal generating circuit outputs display data corresponding to the drain line selected by the time division switch from the output terminal. As a result, a display signal corresponding to the display data is applied to the liquid crystal inside the liquid crystal panel, and thus, gradation display is implemented. Thus, it becomes possible to make the number of output terminals of the source signal generating circuit ⅓ of the number of drain lines (=number of horizontal pixels) in the liquid crystal portion in accordance with the RGB time division driving system, and it also becomes possible to reduce the number of source signal generating circuits in comparison with conventional line sequence driving systems. In addition, it also becomes possible to reduce the number of connection terminals between the substrate where the liquid crystal display portion and the time division switch are formed and the source signal generating circuits to ⅓ of conventional line sequence driving systems, and thus, it becomes possible to implement a liquid crystal display device with higher precision and higher resolution.